1. Field of the Invention
This invention relates to a process for the production of an unsaturated glycol diester from a conjugated diene compound and, more particularly, it is concerned with a process for the production of an unsaturated glycol diester comprising reacting a conjugated diene compound, carboxylic acid and molecular oxygen in the presence of a solid catalyst.
2. Description of the Prior Art
The above reaction is known. In particular, when the carboxylic acid is acetic acid, the reaction may be depicted illustratively as follows: ##STR1## wherein R.sub.1 to R.sub.6 are individually a hydrogen atom or a hydrocarbon group, preferably an alkyl group having 1 to 6 carbon atoms.
Unsaturated glycol diesters are very useful as raw materials for various chemical processes. Above all, 1,4-glycol diesters are particularly important as raw materials for preparing organic solvents such as tetrahydrofuran or synthetic resins such as polyurethane resins and polybutylene terephthalate and various proposals have hitherto been made for the production of the same.
In the process for the production of 1,4-glycol diesters, it has been considered desirable to use a palladium type catalyst. For example, in U.S. Pat. No. 3,755,423, 1,4-diacetoxy-2-butene is obtained with high conversion as well as high selectivity by reacting 1,3-butadiene with acetic acid using a solid catalyst containing palladium, at least one of antimony and bismuth and at least one of tellurium and selenium.
Even in the case of using this catalyst, however, the catalyst efficiency, in particular, the palladium efficiency (Mols of diacetoxybutene formed/Catalyst palladium atom hour) is quite low and unsatisfactory in comparison with the catalyst for the synthesis of vinyl acetate by ethylene process which has already been practiced on a commericial scale as a reaction of this type.
A representative patent of Mitsubishi Chemical Company, Japanese Patent Public Disclosure No. 11812/74, reported that the addition of a small amount of tellurium to the Pd/C catalyst results in a dramatic increase in activity for acetoxylation with high selectivity to 1,4-diacetoxy-2-butene (92%).
On the other hand, BASF's patent, Japanese Patent Public Disclosure No. 63119/76, reported that carbon-supported palladium telluride (Pd4Te/C) catalyst, which is prepared with a controlled ratio of Pd to Te and gave no diffraction line of metallic palladium in X-ray analysis, shows good activity for acetoxylation.
Both palladium efficiency for diacetoxybutenes (DAB) formation over Pd-Te/C (8.4 mol-DAB/g-atom Pd/Hr) and Pd4Te/C catalyst, (6.4), however, remained at an insufficient level as a commercial catalyst.
Other patents in this area include U.S. Pat. Nos. 3,671,577; 3,922,300; 4,075,413; 4,121,039 and the following Japanese Patent Public Disclosure Nos.:
47-39003 PA0 47-39004 PA0 47-39006 PA0 47-31919 PA0 49-101322 PA0 49-11813 PA0 50-51094 PA0 50-51095 PA0 51-149220 PA0 52-28495
Thus the prior art has taught that in the preparation of solvents such as 1,4-butanediol from butadiene, the key to the process is the initial acetoxylation step wherein a carbon supported Pd-Te catalyst system is used.